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Cranberry juice: the facts

Concerns about the overuse of antibiotics and the development of antibiotic resistance have contributed to growing interest in non-pharmacological alternatives for the prevention and treatment of infections. The successful use of cranberry juice to prevent and treat urinary tract infections (UTIs) has led to its endorsement by health care professionals. This article examines what is known about its effect on the lower urinary tract and considers what advice should be given to those planning to take it.

Concerns about the overuse of antibiotics and the development of antibiotic resistance have contributed to growing interest in non-pharmacological alternatives for the prevention and treatment of infections. The successful use of cranberry juice to prevent and treat urinary tract infections (UTIs) has led to its endorsement by health care professionals. This article examines what is known about its effect on the lower urinary tract and considers what advice should be given to those planning to take it.

Urinary tract infection UTIs are common (Reid, 1994) but are more prevalent in women than in men (Lipsky, 1989), probably because a woman's urethra is shorter than a man's and anatomically closer to the anus. UTIs are also more prevalent in older people.

How does cranberry juice work? In North America, cranberry juice has been used to prevent and treat UTIs since before the advent of antibiotic treatment. There were many theories about how it worked. It was thought that it changed the pH of the urine, which impaired the bacteria's ability to multiply. Another postulated theory was that hippuric acid levels were responsible for the therapeutic effect. These theories have now been superseded.

Bacteria attach themselves to human cells by way of projections made up of complex sugar molecules called fimbriae. Specific Escherichia coli fimbriae are associated with certain sites of infection. For example, uropathogenic E. coli has been shown to bind specifically to uroepithelial cells. While it is by no means the only infecting organism, E. coli is implicated in a high percentage of urinary tract infections - 85% according to Sobel (1991). Evidence also suggests that some people possess unique receptors for P-fimbriated bacteria on their uroepithelial cells, making them more susceptible to adherence and subsequent infection (Petri and Mann, 1995).

Zafriri et al (1989) concluded that there were two independent inhibitors of E. coli fimbriae. Type I fimbriated E. coli was found to be inhibited by the presence of fructose, but they were unable to draw firm conclusions about the compound that inhibited P-fimbriated E. coli.

Ten years later Howell et al (1998) reported that condensed tannins - specifically proanthocyanidins, which are found in cranberries, blueberries and other vaccinium fruit species - appeared to be the main component preventing the attachment of P-fimbriated E. coli to the walls of the urinary tract.

When to use cranberry juice Although there is evidence that the adherence of E. coli is affected by cranberry juice, this is not the case with other organisms. Clients should therefore be advised that cranberry juice is not effective against all urinary tract infections (Schmidt and Sobota, 1988). Nor is it clear whether cranberry juice is solely preventive or whether it can be used curatively.

Avorn et al (1994) produced a significant and well-designed study to determine the effect of the regular ingestion of cranberry juice on bacteriuria and pyuria in elderly women. They concluded that long-term cranberry therapy had a more pronounced effect on converting urine samples out of a bacterial/pyuric state than in preventing the development of UTI.

However, care needs to be taken in applying these results to the general population because there are significant epidemiological differences between women of reproductive age who have UTIs and the elderly women in this study.

People who experience repeated UTIs, or those with long-term catheters, may benefit from drinking cranberry juice. However, clients should be advised not to rely solely on cranberry juice as a treatment and to seek medical advice if their urinary symptoms persist. As research evidence accumulates, nurses will need to ensure that they are able to appraise the latest information.

Dosage advice and length of treatment It is common practice to suggest that a glass of cranberry juice should be taken in the morning and evening, and that it should be drunk straight down rather than sipped. The rationale for this is that it increases the concentration of tannin in the urine.

Howell and her research team (1998) estimated that the amount of condensed tannin in a 300ml glass of cranberry juice, consumed on a daily basis, should help to prevent E. coli from adhering to the bladder wall. Avorn et al (1994) also used 300ml of cranberry juice, although they did not specify whether it was taken in a single dose.

Schmidt and Sobota (1988) found that maximum antiadherence occurred within hours of the ingestion of cranberry juice.

Further research needs to be carried out to identify the effect of regular ingestion on prevention and to clarify the amount of juice necessary to reach therapeutic levels.

It has been argued that the lower the cranberry concentration, the greater the volume required, which has cost implications. It has been suggested that the concentration required may be much less than previously thought (Schmidt and Sobota, 1988), but as yet no firm conclusions can be drawn.

Who may not benefit? Client assessment necessarily precedes any treatment suggestions as some people may not benefit from cranberry juice therapy. Those with gastro-oesophageal reflux disorders, gastric or duodenal ulcers and interstitial cystitis are particularly sensitive.

It has also been shown that acid juices should be avoided by people with rheumatoid arthritis, who may find that they exacerbate joint pain.

People with diabetes should be told specifically that sugar-free juices are available, as should those on calorie-controlled diets.

Travelling with cranberry juice Cranberry juice is not available in some countries, and although tablets and capsules are easy to transport it is not possible to ascertain how effective they are in comparison with the pure juice.

A wide range of products is available, but it is difficult to compare the concentration of tablets. The use of tablets and capsules must therefore remain a matter of client choice.

Professional considerations Health care professionals have little control over the information that is available in the public domain. They are, however, accountable for how they use information and for the advice they give. According to the

UKCC code of conduct (1992), nurses are charged to 'act always in such a manner as to promote the interests and well-being of patients and clients'.

It has been argued that advising a client to drink cranberry juice is no more controversial than giving dietary advice (Nazarko, 1995). However, nurses are expected to ensure that all their practice is not only safe but also up to date and based on research. With nurse prescribing becoming more widespread, attention will continue to focus on the advice nurses give to clients. If a client is not given sufficient information and suffers in some way as a result, he or she may be entitled to pursue a case of negligence.

Some clients may also consider the therapy expensive. This raises the question of whether cranberry juice should be available on prescription in the community as it is in some hospitals.

Conclusion There is evidence that the adherence of the organism responsible for a high proportion of UTIs can be impaired by cranberry juice. This supports the use of cranberry juice as a preventive therapy, but no quality evidence is available to support its use as a method of treatment (Jepson et al, 2000). Nurses who wish to recommend cranberry juice should be aware of this.

They should also be aware of the groups of clients who may be adversely affected by cranberry juice and should discuss with clients the variety of opinions on how and when it should be taken.

Many questions remain unanswered and more research on when, how often and how much cranberry juice is needed for a therapeutic outcome would be welcome.

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